Samples were collected along a transect from Hawaii to Alaska during August 2017 as part of the CDisK-IV (KM1712) cruise on R/V Kilo Moana (Fig. 1 ). The five stations along the transect were designed to sample subtropical, transition zone, and subpolar waters. A rosette of Niskin bottles equipped with CTD (conductivity, temperature, depth) and other sensors for coccolithophore and biogeochemical parameters and a vertically integrated plankton tow were collected at each station. Further plankton tows were conducted at four additional intermediate stations (Supplementary material).
A 0.5 m diameter net with 90 µm mesh size was used throughout; based on previous work this mesh size should provide a good estimate of both pteropod18 (link),77 and foraminiferal78 biomass. The sampling strategy was designed to capture an integrated sample of all foraminifera, pteropods, and heteropods from juveniles to adults living throughout the upper water column. The net was towed from the surface down to a specified maximum depth within the water column, and then back to the surface in a continuous manner following an oblique trajectory through the water column. The maximum depth was determined from the fluorescence profile of the preceding CTD cast, and was selected to ensure the net sampling captured well below the base of the chlorophyll maximum and ranged from 150 m in the most northerly subpolar sites to 300 m in the subtropical region (TablesS1 , S2 ). The volume of water represented by each net tow sample was calculated by multiplying the net area by the distance traveled as determined by a flowmeter. For the vertically integrated values, the integration is carried out from the surface to the maximum depth of the tow.
After collection, samples were preserved in a 4% formalin seawater solution, buffered to a pH of ~8.1 with hexamethylenetetramine73 (link). Samples were split with a Folsom splitter or a McLane rotary splitter (splitting error <4%). Large pteropods and heteropods (>1 mm) were picked and quantified before splitting. Half of the split sample was transferred into ethanol solution in the laboratory for the analysis of pteropods and heteropods.
Water samples from rosettes of Niskin bottles equipped with CTD (Sea-Bird SBE 9) were collected at different depths throughout the photic zone and including the chlorophyll maximum depth.
A 0.5 m diameter net with 90 µm mesh size was used throughout; based on previous work this mesh size should provide a good estimate of both pteropod18 (link),77 and foraminiferal78 biomass. The sampling strategy was designed to capture an integrated sample of all foraminifera, pteropods, and heteropods from juveniles to adults living throughout the upper water column. The net was towed from the surface down to a specified maximum depth within the water column, and then back to the surface in a continuous manner following an oblique trajectory through the water column. The maximum depth was determined from the fluorescence profile of the preceding CTD cast, and was selected to ensure the net sampling captured well below the base of the chlorophyll maximum and ranged from 150 m in the most northerly subpolar sites to 300 m in the subtropical region (Tables
After collection, samples were preserved in a 4% formalin seawater solution, buffered to a pH of ~8.1 with hexamethylenetetramine73 (link). Samples were split with a Folsom splitter or a McLane rotary splitter (splitting error <4%). Large pteropods and heteropods (>1 mm) were picked and quantified before splitting. Half of the split sample was transferred into ethanol solution in the laboratory for the analysis of pteropods and heteropods.
Water samples from rosettes of Niskin bottles equipped with CTD (Sea-Bird SBE 9) were collected at different depths throughout the photic zone and including the chlorophyll maximum depth.
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